A) Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display capable of providing a high contrast ratio using a monochromatic light source.
B) Description of the Related Art
A super-twisted nematic (STN)—liquid crystal display (LCD) has been used as a liquid crystal display unit of a high duty ratio. One type of STN-LCD is a blue color mode display device. A so-called blue color display, in which blue color is presented when a voltage is not applied and white color is presented when a voltage is applied, can be made by disposing a polarizing axis of an analyzer at 30 degrees in a counter-clockwise direction relative to long axes of liquid crystal molecules on an optical output side and by disposing a polarizing axis of a polarizer at 30 degrees in a clockwise direction relative to long axes of liquid crystal molecules on an optical input side, for the polarizing plates disposed above and under the liquid crystal cell.
JP-A-2004-62021 proposes to improve light shielding performance in a cut-off state by making liquid crystal composition of STN-LCD of the blue color mode contain dichromatic pigment. As another means for improving light shielding performance, there is a method of using a compensation plate.
STN-LCD of the blue color mode generally uses a white color back light. If a monochromatic light source such as a light emitting diode (LED) is used, it is possible to provide a mode in which a back light color becomes a display color in a normally black state, by lowering a minimum value of transmission factor in the absence of applied voltage at a wavelength of emission peak of the back light and making the back light transmit at its wavelength of peak emission in the presence of applied voltage.